1. Field of the Invention
The present disclosure relates to a plasma ion source and a charged particle beam apparatus.
2. Description of the Related Art
Conventionally, a configuration for a plasma ion source is known, in which a flow restrictor is provided for restricting flow of gas introduced into a plasma chamber to generate voltage drop between a gas supplier and plasma in gas maintained at high pressure so as to suppress arc discharge (for example, JP-A-2011-142081).
There is known another configuration for a plasma ion source, in which different ion species are generated using a plurality of different types of gases (for example, JP-A-2013-120750).
The plasma ion source of the related art introduces raw gas into a plasma generation chamber and high frequency is applied to a work coil provided around the plasma generation chamber, thereby generating plasma. The plasma ion source applies an acceleration voltage to the plasma in order to provide an acceleration energy to ions emitted from plasma.
The pressure of the plasma generation chamber is about 0.1 Pa to 10 Pa and the pressure of a gas introduction insulation unit is equal to or greater than that of the plasma generation chamber. In this pressure range, discharge is easily generated. In addition, since plasma has conductivity, when plasma enters the gas introductory insulation unit, discharge may be immediately generated.
The plasma ion source of the related art ensures insulation by increasing the pressure of gas or increasing a distance between electrodes.
However, when the distance between the electrodes increases, the size of the plasma ion source increases and costs required for configuration increase. Meanwhile, when the pressure of gas increases, conductance decreases and thus a time required for vacuuming after gas emission of the plasma ion source or a time required for gas replacement when a plurality of different types of gases is used increases.